At present photon detection is carried out with solid state devices, vacuum photo multiplier tubes (PMTs) or hybrid photon detectors (HPDs). These instruments also provide fast signal timing information necessary in different fields of science and engineering. In high energy particle physics and nuclear physics experiments the time precision limit for the current systems consisting of particle detectors based on PMTs or HPDs and common nanosecond technology electronics (amplifiers, discriminators, and time-to-digital converters) is about 100 ps (FWHM).
However, it is well known that timing systems based on radio frequency (RF) fields can provide precision of the order of 1 ps or better (see e.g. E. K. Zavoisky and S. D. Fanchenko, Physical principles of electron-optical chronography, Sov. Phys. Doklady 1 (1956) 285 and A. M. Prokhorov and M. Ya. Schelev, Recent research and development in electron image tubes/cameras/systems, International Congress on High-Speed Photography and Photonics, Proc. SPIE 1358 (1990) 280).
Streak cameras, based on similar principles, are used routinely for measurements in the picosecond range (see for example D. J. Bradly, Ultra-short Light Pulses, Picosecond Techniques and Applications, in Topics in Applied Physics, 18 (1977) 17), and have found an increasing number of applications, in particular, in particle accelerators, permitting both precise measurements and instructive visualizations of beam characteristics and behavior that cannot be obtained using other beam instrumentation, (see for example K. Scheidt, Review of Streak Cameras for Accelerators: Features, Applications and Results, Proceedings of EPAC 2000, Vienna (2000) 182).
A Circular Scan Streak Tube (CSST) systems have been proposed for detecting, recording and temporally resolving optical events on the order of picosecond. Much of the investigation in this field has been conducted as part of developing a space borne laser ranging system.
Several possible kinds of readouts for circular scan streak tubes have been considered. The Photochron IIC streak tube as reported in 1984 included a phosphor screen at the output of the tube, covered by a fiberoptic faceplate. The streaked output images were recorded photographically on film. (See W. Sibbett et al, “Photochron IIC streak tube for 300 MHz circular-scan operation,” SPIE Vol. 491 High Speed Photography (Strasbourg 1984)). This method provides a data record length limited to a single scan.
Later, improved signal detection was reported in W. Sibbett and W. E. Sleat, “A Photochron IIC Circular-scan Streak Camera with CCD Readout”, SPIE Vol. 674 High Speed Photography (Pretoria 1986), pp 543-558 and A. Finch, et al, “Electron-sensitive CCD Readout Array for a Circular-scan Streak Tube,” SPIE Vol. 591 Solid State Imagers and Their Applications (1985), pp 31-37. Both of these papers describe the Photochron IIC as a system including a circular array target comprising an array of photodiodes as sensing elements and a CCD shift register to read out the resulting charge. While sensitivity was improved, this arrangement is no less limited in record length to data collected over a single circular scan of the electron beam. After one scan, it is necessary to blank the writing beam, or deflect it off of the electron-beam-sensitive portion of the target to avoid overwriting.
C. B. Johnson, et al, “Circular-scan streak tube with solid-state readout”, Vol. 19, No. 20 Applied Optics (Oct. 15, 1980) describes a circular-scan streak tube (CSST) having a circular photodiode array as a sensing element. The array is optically fiber-coupled to the output phosphor screen of the tube. The array readout circuitry is gated or triggered responsive to the first (start) and second (stop) laser pulses to record first and second streaked output signals, respectively, on the readout array, for measuring the time between the laser pulses. Thus, the acquired data is single-shot rather than continuous recording.
A commercial streak camera and readout system is the Hadland 2DR system, described in D. L. Bowley, “Measuring Ultrafast Pulses,” Lasers & Optronics, September 1987, pp 81-83. The Hadland 2DR target employs a rectangular area CCD array, optically fiber-coupled to the camera. It apparently operates in a single-scan, triggered mode.
Philip S. Crosby, “Circular scan streak tube with electronic memory and readout” U.S. Pat. No. 4,916,543, describes a circular scan streak tube system for recording fast optical data having a first array of detection elements and a second array of corresponding storage elements. Changes in the scanning electron beam current representing optical events are detected and stored in the first array. The first and second arrays are segmented into two halves for continuous operation. Data stored in one half of the first array is transferred into the corresponding storage elements, while new data is written into the second half of the first array. Data stored in the first array is transferred in parallel to the second array. After a triggering event, the data are shifted circumferentially through the second array for output as serial data. The target is formed in a unitary planar semiconductor substrate having a buried channel for storing and conducting electric charge representing the stored data. In this way it enables detecting and storing event signal data over a time interval equal to several times the period of the electron scan. It provides averaged and slow information.
Daniel Joseph Bradley, “Electron-optical image tubes and streak cameras” U.S. Pat. No. 4,327,285, describes an improved method and apparatus for the study of optical phenomena generated by picosecond pulses and for the study of the pulses themselves. A record is obtained of repetitive optical phenomena having durations in the picosecond or sub-picosecond range by synchronizing the deflection of the electron image in an electron-optical streaking image tube with the repetition rate of a pulse train from a continuous wave mode-locked laser which supplies such pulses to the tube. Synchronization may be effected by supplying a reference frequency signal both to the laser and to the deflection electrodes in the image tube. The signal applied to the deflection electrodes may comprise a synchronized sinusoidal voltage signal and a slowly varying bias voltage signal. An optical multi-channel analyzer may be used at the output of the image tube, linked to an oscilloscope or pen recorder. It provides slow information.
Daniel Joseph Bradley, “Electron-optical image tubes” U.S. Pat. No. 3,973,117, describes an electron-optical image tube which avoids the limitations imposed by photographic and image storage techniques and which enables a direct linear intensity profile of a pulse train to be obtained. The image tube, instead of having a phosphor screen, has a disc with one or more slit apertures and photoelectron image is scanned across the aperture or apertures. Time spacing of the light pulses can be adjusted so that the time of the image tube coincides with the fixed aperture or apertures in the disc when a continuous circular scan is used. Maximum transmission of photo-electrons through the aperture is thus obtained, and these photo-electrons are collected and multiplied by an electron-multiplier mounted on the end wall of the image tube. The resulting electrical signal, amplified if necessary, is recorded for example with a pen recorder or oscilloscope. In this way it enables detecting and storing event signal data over a time interval equal to several times the period of the electron scan. It provides slow information.
Yutaka Tsuchiya, “Device for measuring extremely diminished intensity of light” U.S. Pat. No. 4,611,920, describes an electron tube device for measuring an extremely diminished intensity of light by superposing a plurality of streaking images of the light beams caused by fluorescence occurring in a phosphor layer where secondary electrons are incident thereon in single photon units. A streaking image is formed by secondary electrons generated within a streaking tube through which electrons generated in a photoelectric layer therein are accelerated to the phosphor layer therein when passing through a micro-channel-plate therein. The superposed streaking images with enhanced brightness are then picked up by a television camera. It provides slow information.
Yutaka Tsuchiya, “Instruments for measuring light pulses clocked at high repetition rate and electron tube devices therefore”, U.S. Pat. No. 4,694,154, describes an electron tube device for measuring light pulses generated at a high repetition rate which includes an electron tube, power supply device and deflection voltage generator. The electron tube has a photocathode, focusing electrode, deflection electrodes, slit electrode, dynodes and a collector electrode positioned within an evacuated envelope. The power supply device supplies voltages to the dynodes and to the focusing and slit electrodes, and the deflection voltage generator supplies deflection voltages to the deflection electrodes which successively change in phase with respect to light pulses impinging on the photocathode so that different portions of the light pulses can be successively sampled. It provides slow information.
With a streak camera operating in the repetitive mode known as “synchroscan”, a typical temporal resolution of 2 ps (FWHM) can be reached for a long time exposure (more than one hour) by means of proper calibration Wilfried Uhring et al., Very high long-term stability synchroscan streak camera, Rev. Sci. Instrum. 74 (2003) 2646.
The Cherenkov radiation have been detected by using synchroscan circular streak camera at early 1980s, A. E. Huston and K. Helbrough, The Synchroscan picosecond camera system, Phil. Trans. R. Soc. Lond. A298 (1980) 287-293. But commercially available streak cameras provide integral or slow information. They have been known as devices for measuring the temporal variation in intensity of a light emission which changes at high speed but in the past they did not find wide applications, including the high energy elementary particle and nuclear physics experiments.
A fundamental limitation of streak tube data readout is that optical events occur and can be recorded as data faster than the data can be readout electronically. This limitation constrains real time recording of optical events to a brief interval triggered by the event to be recorded.
Accordingly, the need remains for a circular scan streak tube capable of real time recording and storing event signal data over a long period of time, preferably hours or days.